A system for regulating the output voltage of an alternator of a vehicle, supplying power to the electrical system of the vehicle and charging the battery, includes a regulator which controls the excitation current of the alternator. The regulator regulates the output voltage of the alternator with respect to a reference voltage which does not vary as a function of temperature. The system also includes a module in which a temperature sensor measures the battery temperature. This module supplies to the regulator an input signal which is a function of the battery voltage and of the measured battery temperature. The regulator maintains this input voltage at a constant value, and the module is such that this regulation causes the battery voltage to vary in accordance with a required regulation law.
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18. A power supply system for an on-board electrical network of a vehicle having a battery, comprising:
a sensing module to generate an output voltage which is a function of a battery temperature and voltage of the battery; an alternator for supplying power to the electrical network and charging the battery; and a regulator, associated with the alternator, for regulating the excitation of the alternator in such a way that the output voltage of the sensing module is maintained substantially at a voltage level that does not change its value when the battery temperature changes.
1. A power supply system for an on-board electrical network of a vehicle, comprising:
a battery; a sensor for measuring a temperature of the battery; a sensing module, connected to the sensor, for generating an output voltage which is a function of the battery temperature and a battery voltage; an alternator for supplying power to the electrical network and charging the battery; and a regulator, associated with the alternator, for regulating the excitation of the alternator in such a way that the output voltage of the sensing module is maintained substantially at a voltage level that does not change its value when the battery temperature changes.
17. A power supply system for an on-board electrical network of a vehicle, comprising:
a battery; means for measuring a temperature of the battery; means, connected to said means for measuring, for generating an output voltage which is a function of the battery temperature and a battery voltage; means for supplying power to the electrical network and charging the battery; and means, associated with the alternator, for regulating the excitation of the means for supplying power in such a way that the output voltage of the means for generating of an output voltage is maintained substantially at a voltage level that does not change its value when the battery temperature changes.
2. A system according to
3. A system according to
a first amplifier stage, connected to the output of the sensor, for receiving the output voltage from the sensor; a second amplifier stage, connected to the battery, for receiving the battery voltage from the battery; and an adder stage, connected to the first and second amplifier stages, for receiving an output voltage from the first amplifier stage and an output voltage from the second amplifier stage.
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The present invention relates to systems for regulating the output voltage of an alternator.
In the context of a vehicle having a heat engine, the function of an alternator is conventionally to supply power to the wiring network of the vehicle and to recharge the battery of the vehicle when the engine is running. However, limitations are placed on the value of the voltage delivered by the alternator, and by the wiring system itself and the battery of the vehicle. In this regard, the output voltage of the alternator must generally vary as a function of temperature, for example according to a law similar to that illustrated in the curve shown in FIG. 1 of the accompanying drawings. FIG. 1 shows the ideal charging profile as a function of temperature, for a lead-acid battery.
In the example illustrated in FIG. 1, the optimum charge of the battery makes it necessary for the charging voltage to vary in a linear manner as a function of temperature over a straight line D having a negative slope (for example -33 mV/°C). It will be noted that the charging current undergoes severe variation once the charging voltage departs from this optimum line. It is therefore important that the charging voltage should follow this optimum line extremely closely.
In addition, the voltage delivered at the output of the alternator is limited to an upper value which is generally on the order of 15 to 16 volts, being 15.2 volts in the example shown in FIG. 1. This limitation is imposed in particular by the lighting equipment where this equipment makes use of filament bulbs. The alternator output voltage is further limited to a lower value, in the region of 13 volts, by the electromotive force of the battery when the latter is discharged.
Generally, in order to obtain regulation of this type, regulators are used which act on the excitation of the alternator as a function, firstly, of the temperature measured by a temperature sensor which is incorporated in the regulator of the alternator, and secondly, of the output voltage of the alternator or the charging voltage of the battery.
This way of achieving regulation is inexpensive, but from a technical point of view is not at all precise. In this regard, the alternator and the battery are separate components, situated in different places within the vehicle, and the variation in temperature of the battery is very slow, while that of the alternator (and therefore also of the regulator) is very rapid.
In order to be able to regulate the charging voltage of the battery correctly, it is desirable to know precisely the temperature of the battery. However, this is not the case with conventional regulators, which make use of the temperature measured directly on the alternator. In addition, regulators which make use of measurement of battery temperature, are expensive at the present time.
An object the present invention is to overcome the above problem and to propose a regulating system of novel construction which enables the voltage delivered by an alternator to be regulated as a function of the temperature of the battery.
According to the invention, there is provided a system for regulating the output voltage of an alternator for supplying power to the electrical system on board a vehicle, and to charge a battery. The regulating system comprises a regulator which controls the excitation current of the alternator, and is characterized in that the regulator regulates the output voltage of the alternator with respect to a reference voltage which does not vary a function of temperature. The system further comprises a temperature sensor module including a temperature sensor, for measuring the temperature of the battery and for delivering to the input of the regulator an input voltage which is a function of the voltage of the battery and of the measurement of the temperature effected by the sensor. The regulator causes the alternator to adjust the battery voltage so that the output voltage of the module is maintained to substantially coincide with a reference voltage. This regulation causes the battery voltage to vary in accordance to the regulating laws.
As is understood, such a system can make use of an inexpensive standard type of regulator having a zero temperature compensation.
In addition, the regulation obtained in the system according to the invention is particularly reliable because it takes into account the measurement of the battery temperature.
Further features and advantages of the invention will appear become clearer upon reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example and with reference to the accompanying drawings.
FIG. 1, already referred to above, is a graph showing the curve of the charging voltage of a battery as a function of temperature, in the particular case of a lead-acid battery.
FIG. 2 is a block diagram of a regulating system in one possible embodiment of the invention.
FIG. 3 is a graph similar to that in FIG. 1, which shows, besides the curve of charging voltage, firstly the input voltage VS delivered to the input of the regulator in FIG. 2, and secondly the curve of the output voltage VT of the temperature sensor in the system of FIG. 2.
FIG. 4 is a circuit diagram showing one arrangement for the sensor module in the system of FIG. 2.
FIG. 5 shows the curve of the voltage at the output of the sensor circuit in the module of FIG. 4.
FIG. 2 shows diagrammatically a battery 1 of a motor vehicle, and its alternator 2 which delivers a charging voltage VB to the battery 1. The regulating system in the circuitry of FIG. 2 comprises a standard regulator 3 together with a module 4, which includes a sensor for measuring the temperature of the battery 1.
FIG. 2 also shows a unit 5 for supplying power to the temperature sensor in the module 4, together with an interrupter 5a for controlling this supply of power.
The temperature sensor module 4 transmits to the input of the regulator 3 a voltage VS, which is a linear combination of the voltage of the battery and a voltage VT which represents the temperature of the battery. Thus:
VS =K1 VB +K2 VT (1)
where K1 and K2 are gains in the circuit of the module 4.
The regulator 3 is programmed in such a way that its thermal compensation is zero. It acts on the excitation Exc of the rotor of the alternator in such a way as to maintain its input voltage VS at a constant level, for example at a level of 14.2 volts ±150 mV, which is a regulating voltage commonly used at 25°C
Since, from (1), the battery voltage VB at the output of the alternator 2 is
VB =(VS -K2 VT)/K1 (2)
The circuitry of the temperature sensor in the module 4 is such that the law whereby the output voltage VT varies as a function of temperature enables the required regulation for the alternator output voltage VB to be obtained.
Consequently, the temperature sensor circuit must have a transfer function g(VB, TB), such that if f(VB, TB) is the transfer function to be obtained, i.e.
f(VB,TB)og(VB,TB)=VS (3)
where TB is the temperature of the battery measured by the sensor and o represents the operation of convolution.
FIG. 3 shows the curve of the charging voltage VB which corresponds to the required transfer function f(VB, TB), together with the voltage Vs and a curve VT which corresponds to a transfer function g(VB, TB) which enables equation (3) to be verified. As shown in FIG. 3, the voltage VT varies in a linear manner between the same values of battery temperature TB as does the voltage VB, i.e. from 0 to 60°C VT increases as a function of temperature from a lower threshold of -1 V to an upper threshold of +1 V.
The regulator 3 is for example a series mono-function regulator of the type such as those sold under the reference YV77 by the company Valeo Equipements Electriques Moteur.
It will also be noted that when the ignition switch of the vehicle is closed by operation of the ignition key, the interrupter 5a remains open so long as the heat engine of the vehicle has not been started to the point at which the charging voltage of the battery is itself high enough for the voltage VS to reach its nominal value.
Reference is now made to FIG. 4, which shows in detail one example of a possible circuit arrangement for the temperature sensor module 4. The module 4 shown in FIG. 4 includes a temperature sensor 4a which delivers a current having an intensity which increases in a linear manner as a function of temperature.
The temperature sensor 4a may for example be a temperature sensor of the type sold by the Analog Device Company under the reference AD 590 JH. This type of sensor behaves as a source of current of 1 μA/° K., designed to operate between -55°C and +150°C, with a relative error of ±0.5°C over this range. Such sensors are capable of being supplied with a voltage between 4 and 30 volts. In the present example, the power supply unit 5 consists of two 9 volt batteries.
The temperature sensor 4a is connected between a power supply terminal supplying the voltage from the output of the power supply unit 5 and a circuit which comprises four branches connected to ground (earth) in parallel, namely one branch which consists of a resistor R1, a second branch consisting of a Zener diode Z1, and two further branches comprising capacitors C1, C2 respectively. The diode Z1 is connected in the passing sense from ground towards the temperature sensor 4a.
The voltage at the common node of these various branches with the temperature sensor 4a is passed to the non-inverting input of an operational amplifier OP1 which is connected as a voltage follower. The output of this amplifier OP1 is injected into an amplifier stage 6, through another Zener diode Z2, which is connected so as to be passing in the direction from the amplifier stage 6 towards the output of the operational amplifier OP1.
As can be seen in FIG. 5, with such a circuit, the voltage VR1 which is passed to the input of the amplifier stage 6 is proportional to the current from the source consisting of the temperature sensor 4a. It therefore increases in a linear manner as a function of temperature. As to the Zener diode Z1, this limits the voltage VR1 to an upper threshold value, while the second Zener diode Z2 limits the same voltage to a lower threshold value.
If for example the resistor R1 has a value of 33 KΩ, this input voltage is 9 volts for a battery temperature of 0°C, and 11 volts for a battery temperature of 60°C In practice, the resistor R1 preferably has a variable value as shown in FIG. 4, so as to enable the slope of the variation in its voltage as a function of temperature to be adjusted.
The capacitors C1 and C2 act as filters and stabilize the first stage of the module 4.
The Zener diode Z1 may for example typically have a Zener voltage of 11 volts, with the other Zener diode Z2 having a Zener voltage of 9 volts. The capacitance of the capacitors C1 and C2 are for example 22 nf and 10 μf respectively.
The voltage Vt at the output of the amplifier stage 6 is passed to one of the inputs of an adder stage 8, in which it is added to a voltage corresponding to the voltage VB which has previously been amplified by a further amplifier stage 7.
The amplifier stage 6, the amplifier stage 7 and the adder stage 8 will now be described.
The amplifier stage 6 comprises an operational amplifier OP2, the non-inverting input of which is connected firstly to the Zener diode Z2 through a resistor R2 of 510 Ω, and secondly to ground through a resistor R3 of 1,000 Ω. The output of the operational amplifier OP2 is connected to its inverting input through a further resistor R5 of 100 KΩ. This inverting input is also connected to ground through a resistance R4 which is variable between 12 and 22 KΩ.
The amplifier circuit 7 includes an operational amplifier OP4, the non-inverting input of which receives the voltage VB through a resistor R11 of 33 KΩ. The end of this resistor R11 which is opposite to that through which the voltage VB is injected is connected to ground through a capacitor C3 of 47 nF, and to a further resistor R12 of 680 KΩ, the other end of which is connected to the non-inverting input of the operational amplifier OP4. This non-inverting input is also connected to ground through a resistor R13 of 680 KΩ. The inverting input of this operational amplifier OP4 is connected to ground through resistor R14 of 18 KΩ, which is in series with a resistance R15 that is variable between 0 and 20 KΩ. It is connected to the output of the operational amplifier OP4 through a resistor R16 of 33 KΩ.
The adder stage 8 includes an operational amplifier OP3, the non-inverting input of which is connected to the output of the operational amplifier OP4 through a resistor R17 of 9.1 KΩ, and secondly to the output of the operational amplifier OP2 through a resistor R6 of 27 KΩ in series with a resistance R7 which is variable from 0 to 20 KΩ. The inverting input of the amplifier OP3 is connected to ground through a resistor R8 of 10 KΩ, and to the output of the operational amplifier OP3 through a resistor R9 of 10 KΩ in series with a resistance R10, which is variable from 0 to 10 KΩ.
The output voltage of the operational amplifier OP3 is the voltage VS. The variable resistance R10 is adjusted according to the gain required. The resistors R15 and R4 also enable the gains K1 and K2 to be adjusted. The resistor R7 enables a gain to be adjusted before the adding stage. The resistor R11 and the capacitor C3 provide filtering for the battery voltage.
In another embodiment, instead of supplying the temperature sensor module 4 at 18 volts, which makes it necessary to make use of two 9 volt batteries, the module 4 is supplied with power at 9 volts, and this enables the alternator and/or the battery to be used for supplying power to the temperature sensor. In this case, the nominal voltage VS which is held constant by the regulator is halved as compared to the value mentioned in the foregoing description, that is to say it is of the order of 7 volts. In order to achieve this, it is only necessary to make appropriate modifications in the values of the resistances of the variable resistors in the module 4, and to use a reference value divided by two in the regulator 3.
In a further modification, instead of dividing the power supply voltage for the module 4 by two, it may also be divided (as may be the other variables) by some other value in the range between 1 and 10.
It is of course possible, within the scope of the invention, to envisage versions other than those already described. In particular, other types of thermal compensation may be provided in the temperature sensor module.
Again, the module 4 may include means for inhibiting the regulator when the battery voltage exceeds a given threshold value, for example 16 volts. Moreover, the regulator 3 can also have a secondary input which is connected to the battery through the ignition switch of the vehicle, and be provided with a telltale lamp, this arrangement being such as to enable the battery voltage to be regulated in a downgraded mode by the regulator 3 in the event of faulty input of the voltage VS.
In the various embodiments described above, the module 4 is constructed with analog-type components. However, it will of course be understood that the module may consist of digital microprocessors, with the connection between the module 4 and the regulator 3 being in this case obtained with the aid of a data bus.
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